Positive crankcase ventilation systems (PCV systems) are known for removing crankcase gases from internal combustion engines (IC engines) and controlling emissions therefrom. Crankcase gases include blowby gases, which are small amounts of fumes and unburned fuel-air mixtures that bypass the pistons and the piston rings during operation of the IC engine.
PCV systems typically route crankcase gases from the crankcase to the intake manifold. The crankcase gases are then combined with the fuel-air mixture and drawn back into the cylinders for combustion. The resulting fumes are ultimately carried to a catalytic converter where they are treated for release into the atmosphere.
A typical PCV system uses a positive crankcase ventilation valve (PCV valve) to meter the flow of crankcase gases from the crankcase to the intake manifold. The PCV valve has an orifice through which the crankcase gases flow. The orifice may be formed within a washer that is insert molded into the body of the PCV valve or otherwise provided by other suitable means. Also, the valve ordinarily uses a plunger to obstruct the flow of crankcase gases through the orifice of the valve. A common design for the PCV valve requires that the plunger is oriented in a manner that manifold vacuum draws the plunger toward the orifice of the valve. The plunger usually has a spring or other biasing member coupled thereto for forcing the plunger away from the orifice. The force of the spring is balanced with manifold vacuum to determine the degree to which the plunger obstructs the flow of crankcase gases. This balance regulates the flow of crankcase gases through the PCV valve to remove crankcase gases from the crankcase at the same rate they accumulate therein.
In particular, crankcase gases typically accumulate within the crankcase at a rate in direct relation to engine speed. For example, the accumulation rate is minimal at engine idle and increases during higher engine speeds. Moreover, the engine speed is typically inversely proportional to manifold vacuum. Manifold vacuum is high at engine idle and decreases at higher engine speeds. A high manifold vacuum may overcome the force of the spring and draw the plunger sufficiently toward the orifice to decrease the flow of gases exiting the crankcase. Alternatively, a lower manifold vacuum may be overpowered by the force of the spring in that the plunger is not drawn as close to the orifice. Thus, crankcase gases are removed from the crankcase at a similar rate as they accumulate therein.
In addition to removing crankcase gases, an open-type PCV system also supplies fresh air to the crankcase. The fresh air is normally drawn from an air intake through a PCV closure tube into the crankcase. Since the incoming air typically has moisture, water may build up within the crankcase. Unfortunately, the presence of water within the crankcase may cause existing PCV systems to fail in cold environments, e.g. environments where the temperature is −40 C or below. Additionally, the presence of water within the crankcase may also cause existing PCV systems to fail when ambient temperatures are at or below freezing. It is known that moisture in the crankcase may mix with blowby gases and then flow through the PCV valve into the intake manifold. As the gases mix with the cold air in the intake manifold, ice may form and block the PCV valve. Meanwhile, blowby gases may continue to enter the crankcase thereby causing positive pressure to build within the crankcase.
The positive pressure can cause an adverse effect known as backflow. Backflow is the condition where flow in the PCV closure tube is reversed. The positive pressure causes crankcase gases within the crankcase to flow through the PCV closure tube into the air intake. Moisture in the crankcase gases may freeze within the air intake as a result of the low temperature of the fresh air and the substantial drop in pressure of the gases as they enter the air intake. A block of ice may subsequently break free and be drawn into the throttle body where it wedges the throttle plate into an open position. Obviously, such an adverse result may cause serious safety problems.
Another problem associated with the build up of positive pressure within the crankcase is that it may cause an engine seal to fail. The compromised seal would then allow motor oil to escape from the engine consequently leading to loss of engine function. Furthermore, the failure of the engine seal may allow blowby gases to escape into the atmosphere without first having been burned in the engine or treated by the catalytic converter. These blowby gases typically contain hydrocarbon and carbon monoxide vapors, which are known to be poisonous to the environment. Consequently, the release of these gases is an undesirable result.
Still another problem resulting from a PCV valve blocked by ice is that crankcase gases may contaminate the motor oil. Low levels of contamination may reduce the life of the oil, whereas higher levels may lead to engine failure. In this regard, sufficient contamination may transform the oil into a heavy sludge thereby depriving the engine of needed oil. As a result, parts of the engine are left unprotected and may subsequently lead to bearing failure. In addition, these parts may also corrode to the extent of causing engine failure.
Solutions have been proposed to address freezing in a PCV system. One such solution is disclosed in U.S. Pat. No. 6,546,921 and includes a heated PCV valve for properly heating the flow of crankcase gases drawn into the intake of the manifold. This solution successfully minimizes freezing of the PCV valve, but does not solve the problem of freezing at other locations in the PCV system, including the inlet to the manifold. Another proposed solution for addressing freezing at other locations in the system involves utilizing the engine coolant to “water-heat” the PCV valve and/or the intake manifold inlet port. This later solution requires the inclusion of additional piping or tubing to direct the flow of engine coolant to a desired location in the PCV system. However, this solution does not allow for accurate control of the amount of heat to be provided to the desired location and is also relatively inefficient and costly.
Still another proposed solution for addressing freezing involves the placement of a heating device in the manifold itself. This device only heats the gases at the location where the fresh air and the crankcase gases mix. The heating device thus fails to provide any heat to the crankcase gases as they flow from the crankcase to the manifold through its inlet. Moisture in the crankcase gases may condense and ice may form as the crankcase gases travel from the crankcase to the discharge port. In this regard, the ice may impede or even completely block the flow of crankcase gases to the intake manifold. As a result, the PCV system may no longer operate properly and the various problems described above may arise. This manifold heating device also suffers from a variety of other problems, including larger failure issues as the wires are soldered directly to weld pads on the heater. These solder connections are more prone to failure.
Therefore, it would be desirable to provide a PCV system that minimizes any freezing issues due to the flow of crankcase gases and allows the PCV system to operate in cold environments. It would also be desirable to provide a PCV system that is more efficient and less costly than prior systems.